prison diary; diary written in prison
A diary or memoir written while the author is incarcerated. Often used in titles of literary or historical works.
彼の獄中記は、過酷な収容所生活を克明に綴っている。
His prison diary vividly records the harsh life in the camp.
Compound of 獄中 (gokuchū, 'in prison') and 記 (ki, 'record, chronicle').